Solid state memory is a standard component of computer systems and of many electronic devices, providing local storage to the electronic circuit that incorporates it. Some examples of solid state memory components are flash EPROM (erasable, programmable read-only memory), SRAM (static random access memory), and DRAM (dynamic random access memory). One useful function of local memory is to hold small amounts of microcode to be used, for example, for programming programmable circuit components, or for running basic assurance tests (BATS) on other the circuit components. Another useful function of local memory is to store user information, e.g. local storage is used by a pager to store telephone numbers and messages, by a fax machine to store communication protocol parameters, by a printer to store fonts, and so on. For reliability and flexibility, the solid state memory used in such applications is non-volatile and modifiable, e.g. SRAM.
Unfortunately, the cost of solid state memory increases almost linearly with its storage capacity. Moreover, since there are physical limitations to known solid state technologies, an increase in the storage capacity of memory corresponds to an increase in its physical size. These limitations present a foreseeable problem with the growing demand for small, sophisticated, portable, and inexpensive devices with substantial storage requirements.
One area in which the limitations of solid state memory are becoming apparent is card-based electronic circuits. For example, circuits embodying or controlling fax machines, modems, cellular phones, printers, cameras, disk drives, and other devices are presently being housed in credit-card sized formats of predefined dimensions that plug into a compatible socket of a laptop computer, PC, or other electronic device. Three standard formats that have emerged for such credit-card-type applications are the PCMCIA formats. A "type III" card measures 10.5 mm in height, 5.6 mm in length and 54 mm in width. The dimensions of a "type II" card are approximately 3.3 mm high.times.85.6 mm long.times.54 mm wide. A "type I" card is a modest 2.5 mm high.times.85.6 mm long.times.54 mm wide.
In contrast to solid state memories, magnetic disk drives in general are becoming smaller, and their cost per megabyte is decreasing. It is therefore advantageous to provide a magnetic disk drive small enough to replace solid state memory in electronic devices, such as printers, and in card-based electronic circuits, e.g. PCMCIA formats. Furthermore, magnetic disk drives are ideal for many of the applications discussed above because they provide modifiable, high density, nonvolatile storage.
Until recently, however, magnetic storage devices have been large too incorporate directly into an application circuit such as those implemented in PCMCIA type card enclosures. Rather, drives have traditionally been peripheral devices communicating with the application through a peripheral interface. Moreover, removable, card-based electronic circuits and many electronic devices in general must remain operational after being dropped or otherwise exposed to external shock. Previous disk drives were unable to withstand large amounts of external shock without suffering damage, because the shock caused the read/write heads and suspensions to slam into the magnetic recording surfaces.
Recently, a number of small disk drives have become available on the market approaching a component-sized storage device. For example, Hewlett Packard offers a 20-40 MB 1.3" KittyHawk drive. In addition, component type drives are disclosed in U.S. Pat. No. 5,264,975, Japanese application nos. 62-270089, 04-291079, and Japanese publication no. 01112586. However, none of these references discusses an architecture for implementing a disk drive as local storage within an electronic circuit, wherein the circuit performs functions unrelated to the operation of the disk drive itself, e.g. a circuit wherein the disk drive stores microcode for use in the operation of the circuit, or wherein messages received by the circuit are stored in the disk drive.